Bending machine



Nov. 22, 1966 J, w ss 3,286,500

BENDING MACHINE Filed Nov. 27, 1965 5 Sheets-Sheet l Nov. 22, 1966 J. WEISS BENDING MACHINE 3 SheetsSheet 2 Filed Nov. 27, 1963 Nov. 22, 1966 J. WEISS BENDING MACHINE 5 Sheets-Sheet 3 Filed Nov. 2'7, 1963 United States Patent BENDIN G MACHINE Josef Weiss, Hagen, Germany, assignor to Heinrich Bartz Kommanditgesellschaft, Dortmund, Germany Filed Nov. 27, 1963, Ser. No. 326,463 Claims priority, application 8*(igrmany, Nov. 30, 1962,

Q 6 Claims. (Cl. 72-219) This invention refers to bending machines for forming loops on round or flat stock or the like and more particularly to bending machines which employ hydraulic cylinders to clamp the workpiece and to actuate the tools.

Various methods have been applied to form loops on flat or band stock, all of which, however, have certain disadvantages. The oldest method which even today is still frequently used, is represented by manually controlled forging. -Its drawbacks include high requirements of human energy, low production per unit time, large dimensional variations, and poor utilization of the heat needed to raise the stock to forging temperature. A number of devices has been developed to mitigate these drawbacks at least to a certain extent.

Benders are known which have a form block around which a movable roller rotates. In rotating the tool, the end of the flat or round bar stock is wrapped around the block, and the loop is formed. The disadvantages of such known devices have been that the loops can be made of circular shape only, and that any variation of loop diameter, or section or thickness of the stock is either impractical or laborious. The specifications covering tool tolerances in such known benders are stringent. Hence, high investment presents another drawback.

As stated above, the known types of benders allow of forming only circular loops. However, many applications require loops of other than circular shape. Heretofore, such loops were obtained by preforming a circular loop in a bender of the aforementioned type and by modifying subsequently such loop to give it the desired form, for instance by means of a suitably shaped die of other than circular contour.

This brings out another drawback of the conventional procedure. To produce non-circular loops, two opera tions and two tools are needed, and a single heating operation is not sufficient. Proper correlation of the two forming stages to supply the desired end product requires a trial-and-error approach and depends on the dimensional variations of the stock. As a result, the dimensional variations of the product will likewise be considerable, which, in turn, will result in a high percentage of rejects.

It is a principal object of this invention to avoid the recited drawbacks and to provide a bender which permits of forming circular, elliptical, oblong or polygonal loops on band or bar stock of steel or other materials, and to perform this shaping process with satisfactory precision and uniformity of results.

Other objects and advantages will be apparent from a consideration of the specification and claims.

The bending machine in accordance with this invention is equipped with a hydraulically actuated centering device for proper adjustment of the workpiece, which cooperates with hydraulic clamping means. For the purpose of this invention, the machine is further provided with a prismatic die block Whose cross section corresponds to the shape of the eye to be formed and which works together with a bender whose roller head is urged by hydraulic pressure against the die block. The bender is moved around said die block in order to wrap thereon the end of the workpiece located between die block and bender head. The hydraulic cylinder acting upon the roller head is in communication with a compensating cylinder Whose piston is loaded by means of an adjustable force acting against the fluid pressure.

The invention permits to produce precisely controllable clamping, holddown, and forming forces in a very compact machine design. Through the use of hydraulics, the operation of the machine can conveniently be automated if desired.

An essential characteristic of the invention is that the hydraulic press cylinder which forces the roller against the workpiece and the die block is in communication with a compensating cylinder whose piston is acted upon against the fluid pressure inside that cylinder by an adjustable force. This feature allows the forming of loops of other than circular shape. During the rotation of the movable roller around the die block, that roller must perform radial motions without incurring excessive or inadequate pressures of application. Such controlled application of the movable roller around the die block is made feasible by the compensating cylinder. The force acting upon the piston of that compensating cylinder assures the maintenance of a pressure as required for the proper function of the tool. By suitable design of the energy source and proper adjustment of the force exerted by it, a radially directed outward motion of the movable roller will produce an increase in roller pressure which, however, remain under adequate control because the yielding of the piston in the compensating cylinder will modify the counteracting force. When in the course of its rotation the roller moves again toward the die block, the force applied to the compensating piston and the energy source acting upon the power cylinder of the movable roller will not permit an undue reduction in the pressure available.

The invention also provides that the die block may have a circular, elliptical, elongated or polygonal contour to form loops of different shapes.

In a preferred embodiment of the novel bender, the piston of the compensating cylinder is controlled by an adjustable spring.

This design of the machine offers the advantage of simplicity. The use of a preset spring for loading the piston of the compensating cylinder also helps to control the rolling operation, a it will permit the movable roller to yield radially, the pressure increase remaining Within set and controllable limits as necessitated by the bending operation. Suitable regulation of the preset range ensures that the minimum pressure necessary for the rolling process is always exerted on the roller tool.

The piston of the compensating cylinder may also be loaded by a controlled fluid pressure or by a preferably exchangeable counterweight. Use of a counterweight instead of the aforementioned spring will permit to further simplify the device and is especially advantageous when elliptical shapes must be formed from sensitive, especially thin, fiat bar stock of steel or other metals. Use of a weight will allow the movable roller to yield without increasing the contact pressure. This presupposes that there is no need to have that pressure increased. The alternate possibility to have a medium of controlled pressure actuate the piston of the compensating cylinder, instead of a weight or spring, opens a wide range of potential applications. For high operating speeds it may become necessary that the movable roller yield very rapidly; especially for much elongated loops or with polygons the motions of the movable roller, and their directions, will change very quickly or to a large degree. For conditions such as these, the use of springs or weights will become impractical, and a properly controlled fluid such as air or gas will be the preferable medium.

In order to obtain an automatic operation cycle, which can be repeated as often as desired, the machine may be equipped with a time switch to control the clamping device, with a pressure switch which responds when a preset clamping pressure has been reached and which controls the hydraulic cylinders and the motion of the forming roller, and with solenoid valves to reverse the hydraulic cylinders and to return the movable roller, the centering device and die being movable longitudinally through properly controlled cylinders, in order to release and replace the workpiece.

A bender thus equipped will permit automatic operation if the workpieces are fed and released automatically. However, the feed and discharge of the workpieces is outside the scope of this invention. Since hydraulic elements are primarily considered for performing the individual functions and motions, simple and reliable means for automation are available. The advantages offered by such automation reside principally in that the formed loops or finished bar ends satisfy'strict requirements as to tolerances and properties. One distinct advantage of the novel bender is, in effect, that the uniform working conditions ensure constant product quality even for high production rates.

To further increase the versatility of the new bender, the level of the clamping device can be varied with reference to the die block, which permits of producing cranked or S-bent loops.

An illustrative embodiment of the bending machine according to the invention is shown, by way of example, in the accompanying drawings, where FIG. 1 is a longitudinal section through the machine;

FIG. 2 shows a section along line IIII of FIG. 1, and

FIGS 3 and 4 show embodiments of various loading means for the piston of the compensating cylinder.

Referring to the drawings, the novel bender has a baseplate 1 to accommodate a workpiece 14. To said base, there is attached a hydraulic cylinder 2 whose piston carries a centering pin 3 for upward movement.

The loops are formed by means of a die block 4 which determines the contour of the loop. Said die block is a prismatic body having a circular, oval, polygonal crosssection, or an elongated contour as shown in FIG. 1. The die block is movable longitudinally, i.e. along its main axis, and is shifted by the hydraulic cylinder 5. The centering device 2, 3 holds the workpiece in such a manner that its end rests on the die block and protrudes therefrom to an extent sufficient for forming a completely closed loop.

To clamp the workpiece, another hydraulic cylinder 6 is provided. This cylinder 6 moves a closing block 13 and forces it upon the workpiece located on plate 1. To shape the loop, a movable roller 8 is pressed on by another hydraulic cylinder 7. The movable roller 8, together with the cylinder 7, is rotatable around a fulcrum located in the main axis of the die block and can be moved into the position shown in dotted lines in FIG. 1. To swing the tool and its cylinder, a hydraulic rotating device 12 is provided. The location of the roller tool and its cylinder indicated by dotted lines 9 corresponds to an angular displacement through about 270 degrees. This rotation suflices for the complete closing of an eye.

When forming loops of oblong or elliptical shape, the tool must be able to yield radially along its main axis, to avoid injury to the workpiece. To this end, the fluid space of cylinder 7 of the roller communicates with a compensating cylinder 10. A flexible hose 11 is employed to connect the pressure chambers of the cylinders. The compensating hydraulic cylinder has a piston 15 acted upon by a pressure spring 16. Spring 16 can be preset by a handwheel or other known device 17. This compensating cylinder permits roller 8 to yield radially when forming loops of oval or elongated contour, whereby the excess hydraulic fluid in cylinder 7 enters the compensating cylinder 10, forcing piston 15 back against the action of spring 16. This will increase the contact pressure of the roller only to a moderate extent which is not harmful for the workpiece. The effective increase is set by selecting the initial stress on spring 16 so as to obtain the increased work-ing pressure required for the lengths of small curvature present. In this fashion, the contact pressure is continuously adjusted to the process requirements by simple means.

Instead of an adjustable spring 16, controlled fluid pressure can be used, as diagrammatically shown in FIG. 3, where 18 indicates a pressure control line communicating with a pressure accumulator 19 filled with hydraulic fluid and containing e.g. a pretensioned nitrogen bag 20.

In the modification illustrated in FIG. 4, the piston 15 in cylinder 10 is controlled by an exchangeable and displaceable counterweight 21.

The hydraulic cylinder 6 of the clamping device is connected to a pressure switch (not shown). Once the required clamping pressure has been obtained, cylinder 7 receives pressure fluid for the rolling tool 8. At the same time, pressure fluid is transmitted to rotating drive 12, and the forming of the loop starts. At the end of the swing or rotating motion of the movable roller and the corresponding cylinders, solenoid valves will so control the pressure fluid in rotating drive 12 and in cylinder 7 that the roller is returned to its original station. Simultaneously, these solenoid valves will control the cylinder 2 of the centering device and cylinder 6 of the clamping device, and holddown plate 13 and center pin 3 are retracted from workpiece 14. Cylinder 2 of the centering device also acts as a valve and, as soon as the centering pin 3 has been retracted fully, it will clear the path of the fluid to cylinder 5 which then retracts die block 4 from the loop which has been formed. The finished piece can now be removed manually or automatically. When the centering pin 3 and the other elements of the bender have returned to their end positions, permitting removal of the workpiece, a time switch is operated which prevents operation of the device until the die block has been reset to operation. Afterwards, or simultaneously with the resetting of the die block, a new workpiece may be inserted in the manner described, and the cycle can be restarded as described.

In simple benders, the last named switch may be manually or pedal operated, and the workpiece are fed 'manually and retrieved manually.

For installing the novel bender in an assembly line conventional automatic devices should be employed to handle the workpieces, and instead of the manual or pedal switch, a second time switch should be provided to correlate the operation of the bender to the timing of the line.

The novel bender described herein-above is not only suited to the forming of spring steel stock or the like which requires heating. The adjustability as to operating pressures of the movable roller, and more especially the automatically changing force of the contact pressure, makes it possible also to work relatively sensitive materials, light metals or the like, in either warm or cold state.

I claim:

1. A bending machine for forming loops of any desired shape on round or flat stock or the like comprising a support for the workpiece, cooperating hydraulic clamping means and hydraulic centering means securing the workpiece on said support, a die block having an equal cross section along its effective length and corresponding to the loop to be formed, a bender comprising a hydraulic cylinder and a roller head resiliently forced against said die block, said bender being supported for rotary movement to wrap the end of said workpiece around said die block, hydraulic means producing the rotary movement of the bender, a hydraulic compensating cylinder communicating with said first hydraulic cylinder, a piston in said compensating cylinder, and adjustable pressure means adjustably and yieldingly loading said piston against the hydraulic fluid pressure, thus equalizing the pressure exerted by said roller head when moving the bender in pressure exerting contact around said die block.

2. A machine as claimed in claim 1 wherein said adjustable pressure means is an adjustable spring in said compensating cylinder acting against said piston.

3. A machine as claimed in claim 1 wherein said adjustable pressure means is a hydraulic fluid.

4. A machine as claimed in claim 1 wherein said adjust'able pressure means is an exchangeable counterweight.

5. A machine as claimed in claim 1 wherein said die block and said centering means are displaceable in the direction of their longitudinal axes.

6. A machine as claimed in claim 1 wherein said clamping means are vertically d-isplaceable with respect to said die to produce S-bent loops.

References Cited by the Examiner 5 UNITED STATES PATENTS 2,986,194 5/1961 De Marco 7 2-215 FOREIGN PATENTS 317,221 4/ 1934 Italy.

10 CHARLES W. LANHAM, Primary Examiner.

R. D. GREFE, Assistant Examiner. 

1. A BENDING MACHINE FOR FORMING LOOPS OF ANY DESIRED SHAPE ON ROUND OR FLAT STOCK OR THE LIKE COMPRISING A SUPPORT FOR THE WORKPIECE, COOPERATING HYDRAULIC CLAMPING MEANS AND HYDRAULIC CENTERING MEANS SECURING THE WORKPIECE ON SAID SUPPORT, A DIE BLOCK HAVING AN EQUAL CROSS SECTION ALONG ITS EFFECTIVE LENGTH AND CORRESPONDING TO THE LOOP TO BE FORMED, A BENDER COMPRISING A HYDRAULIC CYLINDER AND A ROLLER HEAD RESILIENTLY FORCED AGAINST SAID DIE BLOCK, SAID BENDER BEING SUPPORTED FOR ROTARY MOVEMENT TO WRAP THE END OF SAID WORKPIECE AROUND SAID DIE BLOCK, HYDRAULIC MEANS PRODUCING THE ROTARY MOVEMENT OF THE BENDER, A HYDRAULIC COMPENSATING CYLINDER COMMUNICATING WITH SAID FIRST HYDRAULIC CYLINDER, A PISTON IN SAID COMPENSATING CYLINDER, AND ADJUSTABLE PRESSURE MEANS ADJUSTABLY AND YIELDINGLY LOADING SAID PISTON AGAINST THE HYDRAULIC FLUID PRESSURE, THUS EQUALIZING THE PRESSURE EXERTED BY SAID ROLLER HEAD WHEN MOVING THE BENDER IN PRESSURE EXERTING CONTACT AROUND SAID DIE BLOCK. 